Track object position during an animation using python script
Object.matrix_world.to_translation() gives you a global (visual) location of the object.  The frame change handler makes the panel "hot" and update on every frame change. 

import bpy

class MocapPanel(bpy.types.Panel):
    """Creates a Panel in the Object properties window"""
    bl_label = "Display Data"
    bl_idname = "OBJECT_PT_hello"
    bl_space_type = 'PROPERTIES'
    bl_region_type = 'WINDOW'
    bl_context = "object"

    @classmethod
    def poll(cls, context):
        return context.object is not None

    def draw(self, context):
        layout = self.layout

        obj = context.object
        pos = obj.matrix_world.to_translation()

        row = layout.row()
        row.label(text="Active object is: " + obj.name)
        row = layout.row()
        row.label(text="object position z is %.2f" % pos.z)

def prop_redraw(scene):
    for area in bpy.context.screen.areas:
        if area.type == 'PROPERTIES':
            if area.spaces.active.context == 'OBJECT':
                area.tag_redraw()

def register():
    #clear handlers for testing
    bpy.app.handlers.frame_change_pre.clear()
    # add a handler to make the area "live" without mouse over
    bpy.app.handlers.frame_change_pre.append(prop_redraw)

    bpy.utils.register_class(MocapPanel)

if __name__ == "__main__":
    register()